Not Applicable.
Not Applicable.
1. Field of the Invention
The embodiments relate generally to well drilling. More particularly, the embodiments relate to the processing of the drilling cuttings, drilling mud, and/or other waste that is generated from a well. Specifically, the embodiments relate to improved methods and apparatus for disposing of deleterious materials from a well using a floating vessel to transport the materials from the well to a final disposal site.
2. Description of the Related Art
In the drilling of wells, a drill bit is used to dig many thousands of feet into the earth""s crust. Oil rigs typically employ a derrick that extends above the well drilling platform. The derrick supports joint after joint of drill pipe connected end to end during the drilling operation. As the drill bit is pushed further into the earth, additional pipe joints are added to the ever lengthening xe2x80x9cstringxe2x80x9d or xe2x80x9cdrill stringxe2x80x9d. The drill string therefore comprises a plurality of joints of pipe. Each pipe joint has an internal, longitudinally extending bore.
Fluid xe2x80x9cdrilling mudxe2x80x9d is pumped from the well drilling platform, through the drill string, and to a drill bit supported at the lower or distal end of the drill string. The drilling mud lubricates the drill bit and carries away well cuttings generated by the drill bit as it digs deeper. The cuttings are carried in a return flow stream of drilling mud through the well annulus and back to the well drilling platform at the earth""s surface. When the drilling mud reaches the platform, it is contaminated with small pieces of shale and rock that are known in the industry as well cuttings or drilling cuttings. Once the drilling cuttings, drilling mud, and other waste reach the platform, a xe2x80x9cshale shakerxe2x80x9d is typically used to remove the drilling mud from the drilling cuttings so that the drilling mud may be reused. The remaining drilling cuttings, waste, and residual drilling fluid are then transferred to a holding trough for disposal. In some situations, for example with specific types of drilling mud, the drilling mud may not be reused and it must also be disposed. Typically, the non-recycled drilling mud is disposed of separate from the drilling cuttings and other waste by transporting the drilling mud via a vessel to a disposal site.
The disposal of the drilling cuttings and drilling mud is a complex environmental problem. Drilling cuttings contain not only the residual drilling mud product that would contaminate the surrounding environment, but also can contain oil and other waste that is particularly hazardous to the environment, especially when drilling in a marine environment.
In the Gulf of Mexico, for example, there are hundreds of drilling platforms that drill for oil and gas by drilling into the subsea floor. These drilling platforms can be used in places where the depth of the water can be many hundreds of feet. In such a marine environment, the water is typically filled with marine life that cannot tolerate the disposal of drilling cuttings waste. Therefore, there is a need for a simple, yet workable solution to the problem of disposing of well drilling cuttings, drilling mud, and/or other waste in an offshore marine environment and in other fragile environments.
Traditional methods of disposal have been dumping, bucket transport, cumbersome conveyor belts, screw conveyors, and washing techniques that require large amounts of water. Adding water creates additional problems of added volume and bulk, messiness, and transport problems. Installing conveyors requires major modification to the rig area and involves many installation hours and very high cost.
Another method of disposal includes returning the drilling cuttings, drilling mud, and/or other waste via injection under high pressure into an earth formation. Injection into deeply-buried rock formations is a relatively recent field. In general terms, the injection process involves the preparation of a slurry within surface-based equipment and pumping the slurry into a well that extends relatively deep underground into a receiving stratum or adequate formation. The basic steps in the process include the identification of an appropriate stratum or formation for the injection; preparing an appropriate injection well; formulation of the slurry, which includes considering such factors as weight, solids content, pH, gels, etc.; performing the injection operations, which includes determining and monitoring pump rates such as volume per unit time and pressure; and capping the well.
The principal advantage of this technique is the potential for stable retention of material within a deeply-buried formation over a geological time span. However, in practice, the injection process is not as simple as it may seem.
First, the material to be injected must be prepared into a slurry acceptable to high pressure pumps used in pumping material down a well. The particles are usually not uniform in size and density, thus making the slurrification process very complicated. In addition, if the slurry is not the correct density, the slurry often plugs circulating pumps. The abrasiveness of the material particles can also abrade the pump impellers causing cracking. Some attempts have been made to use the circulating pumps for grinding the injection particles by purposely causing pump cavitation. However, using the pumps for grinding shortens the life of the pump. Hard cakes also can build up in tanks and create circulation problems. Therefore, it is known that a uniform particle size of less than 300 micron must be maintained for proper formation injection at the well site. However, maintaining such consistency with hard and soft materials is very difficult.
Second, space on offshore platforms is at a premium and therefore injection equipment must be compact and as lightweight as possible. Also, the equipment is most often placed in hazardous areas near the well bore where large horsepower internal combustion engines are not permitted due to the possibility of high gas concentration. Therefore, any additional equipment on the offshore platform used for injection must also meet stringent explosion proof requirements for such areas of the rig.
Until now, injection has not gained wide acceptance in offshore drilling operations such as in the North Sea, primarily due to the problems discussed above and the inefficiency and ineffectiveness of the injection processes. Injection failures have occurred primarily due to the inability to fine tune the injection process by providing particle size control, uniform slurry density, and to provide volume and pressure control over the injection process. Additionally, locating an adequate stratum or formation for the injection has also been difficult. As a result, most offshore drilling operators in the North Sea have banned the practice and have resorted to using expensive synthetic drill fluids.
In order to provide a more efficient and cost effective method of processing drilling cuttings, drilling mud, and/or other waste for disposal, the present invention has been developed. Other objects and advantages of the invention will appear from the following description.
The preferred embodiment provides an improved method and apparatus for processing well deleterious material on a floating vessel during transportation from an offshore well to a disposal site. Deleterious material can include, but is not limited to, drilling cuttings, drilling mud, and/or other waste products, or any combination thereof. It should be appreciated that processing can include, but is not limited to, slurrification, agitation, separation, and/or chemical treatment, or any combination thereof. The vessel contains equipment for the processing of the deleterious material. Such equipment includes, but is not limited to, slurrification equipment, storage tanks, and/or agitation equipment, as well as transfer equipment such as flow lines and vacuum or pump means. The deleterious material is transferred from the well to the storage tanks on the vessel. The vessel then transports the material to a disposal site, such as an injection well rig. During transportation, the deleterious material is processed. Once at the disposal site, the deleterious material is then transferred from the vessel to the disposal site. Thus, using the vessel to process the deleterious material during transportation to the disposal site saves the operation time and equipment costs associated with processing at the offshore well or at the disposal site. Including the processing equipment on the vessel also saves needed space at the disposal site, especially in the context of an off-shore injection well.
In another embodiment, the deleterious material is transferred from the well to a floating storage vessel next to the well. This saves space on the well rig platform that is normally used for storage tanks. The deleterious material is then transferred from the floating storage vessel to the floating vessel for transportation from the well to the disposal site. The method then proceeds as in the preferred embodiment.
In another embodiment, the floating vessel is equipped with chemical treatment units that further process the deleterious material. The chemical treatment processes are also performed on the vessel during transportation to the disposal site.
In yet another embodiment, the floating vessel is equipped with treatment units that separate and recycle drilling mud from the drilling cuttings, waste, or other deleterious material. The recycling process may also be performed on the vessel during transportation to the disposal site, but may also be performed at the offshore well.
Thus, the preferred and alternative embodiments comprise a combination of features and advantages that enable them to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred and alternative embodiments, and by referring to the accompanying drawings.